>However, like practically every other company on earth that invents private
>character sets (with the notable exceptions of Apple and IBM), they do not
>document them except by printing a table. The characters are accompanied by
>neither names nor descriptions, nor codes (like IBM's GCGID)to identify them
>and thus distinguish them from other characters with similar appearance.

Actually the Unicode book does try. Not as comprehensively as anyone would
like, but it's a start.

>> I am fairly familiar with the mathematical notation, and there is
>> certainly no commonly used mathematical symbol pair "small letter a with
>> underbar" and "small letter o with underbar".
>>
>Of course I am curious about this too. I notice that Unicode has Capital
>and Small Letter B with underbar (at U+1E06,1E07).

I don't know what those are for.

>Ditto for L (1E3A, 1E3B), N (1E48,1E49), R (1E5E,1E5F)

Transliteration of some letters in Dravidian languages like Tamil.

>T (1E6E,1E6F), Z (1E94,1E95), as well as small h (1E96)

Transliteration of Ancient Egyptian and other Semitic languages.

. And there is a small letter d with stroke and underbar
>at U_20AB (the Vietnamese Dong sign).

Does not require the line below, I think.

>But no A or O.

These are problematic. I tried to use º to write Nº in the French version
of an ISO document recently and Alain LaBonté told me that it was not
acceptable to have a line below, so I had to use the degree sign for N°. I
don't know what this means for fuzzy or precise online searches, since º
has alphabetic value and ° does not.

In Ireland, of course, we need a superscript c for the extremely common
abbreviation for Mac/Mc. The glyph may have no line, or it may have a line,
or it may have a dot below.